Adjustable inductor



March 29, 1966 w. F. GLCVER ETAL 3,

ADJUSTABLE INDUCTOR I Filed July 9, 1963 SylAL L orig Inventors WILLIAM F. CLOVER ACK c. a

F/GZ.

United States Patent 3,243,745 ADJUSTABLE INDUCTOR William Frank Glover and Jack George Bendall, London, England, assignors to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Filed July 9, 1963, Ser. No. 293,605 Claims priority, application Great Britain, July 11, 1962, 26,651/ 62 2 Claims. (Cl. 336-83) This invention relates to adjustable inductors using pot shaped cores of magnetic material, and to a method of their assembly.

The present trend towards smaller components introduces a number of conflicting requirements amongst which are reduced overall dimensions combined with a maximum ratio of inductance to resistance, ease of manufacture and of assembly.

According to the invention there is provided an adjustable inductor including a pot core of magnetic material having a central boss, and a winding positioned within a cavity of the core "by means of a washer of flexible insulating material, the central hole of the washer having a smaller diameter than the outer diameter of the boss.

According to the present invention there is further provided a method of assembling a winding for an adjustable inductor within the cavity of a pot core, which includes the steps of inserting, into the cavity, a flexible insulating washer having an inner diameter smaller than the outer diameter of the inner boss of the core, and placing a winding in the cavity in contact with the washer.

The invention will now be described with reference to the accompanying drawings in which:

FIG. 1 shows a longitudinal partial section through an adjustable inductor; and

FIG. 2 is a plan view of the inductor assembly.

Referring to FIG. 1 the two half shells forming the magnetic core and main body of the inductor are indicated by 1 and 22. They may be of any suitable magnetic material, for example ferrite. These half-cores abut along the faces 2 and can be fixed to each other by any convenient cement or adhesive. An air gap 3 is provided between the central bosses of the half-cores and determines the minimum value of the inductance of the coil.

A' movable slug 4 also of magnetic material, is arranged within the cylindrical bore of the core. The slug can be moved axially by means of a screw 6 cooperating with a nut 8 and brought into a position to bridge the air gap of the core and thus increase the inductance of a winding disposed within the cavity formed by the two half-cores.

Base 12, of ceramic material, is attached to the core 22, and is provided with terminals 13 for the lead out wires of the winding 5. It might also be provided with means for securing it to a printed circuit board. The base 12 can, if required, be mounted on the opposite end of the core assembly, so that the adjustment of the slug can be carried out through the surface on which the inductor is mounted. Hole 11 is provided for this purpose in the base 12.

The ratio of reactance to resistance of the winding is termed the Q factor of the inductor and is a measure of its efiiciency. To keep the latter high, for a given size of core, the volume of the winding 5 must be a maximum. In conventional arrangements the winding 5 is wound on a bobbin or former which locates the winding on the core. Bobbins however take up space and reduce the volume of the winding and thereby the Q factor.

In the winding of FIG. 1 no bobbin is used, the winding being self supporting. Various techniques for producing such windings are known.

The winding 5 is located within the cavity of the core 1 by means of washers 14 having their inner and outer edges serrated. The outer edge of the upper washer is visible in the View shown in FIG. 2. The washers are made for example, of plastic material or of mica. The inner serrated edges 15 of the washers are of smaller diameter than the outer diameter of the central bosses 16 of the half-cores 1 and 31. When the washers are forced over the bosses 16 the serrations 15 are bent back by the core providing a curved surface which locates the inner surface 17 of the winding and provides a uniform gap between the bosses 16 and the winding. The outer serrated edge 18 of the washer 14 is of larger diameter than the maximum diameter of the winding cavity in the core 1. These serrations are also folded back by the core as is indicated at 19 in FIG. 1, except in those parts shown in FIG. 2 where the outer wall of the core 1 is cut away to provide channels 20 through which the leadout wires 21 of the winding are taken for connection to terminals 13. In these channels the outer serrations 18 of the washers are not folded back and act as guides or fanning strips for the wires. The pitch of the serrations is chosen to give the desired number of supporting points for the leadout wires.

It is to be understood that the foregoing description of specific examples of this invention is not to be considered as a limitation on its scope.

What we claim is:

1. An adjustable inductor, comprising:

a pot core formed of two half-shells of magnetic material, said pot core having a central boss and an outer wall, said boss and said wall defining therebetween an annular cavity;

a winding, having lead-out wires;

means for centrally positioning said winding within said cavity about and spaced from said central boss, said means including a washer of flexible, insulating material interposed between said pot core and said winding, at each end of said winding, said washers having serrations about the inner and outer diameters thereof, all of said inner serrations and most of said outer serrations being bent and disposed between said walls and said winding.

2. An adjustable inductor, according to claim 1,

wherein:

said lead-out wires extend radially and are disposed within the serrations of said outer diameter.

References Cited by the Examiner UNITED STATES PATENTS 5/1934 Strait 336192 1/1964 Arita 336-136 

1. AN ADJUSTABLE INDUCTOR, COMPRISING: A POT CORE FORMED OF TWO HALF-SHELLS OF MAGNETIC MATERIAL, SAID POT CORE HAVING A CENTRAL BOSS AND AN OUTER WALL, SAID BOSS AND SAID WALL DEFINING THEREBETWEEN AN ANNULAR CAVITY; A WINDING, HAVING LEAD-OUT WIRES; MEANS FOR CENTRALLY POSITIONING SAID WINDING WITHIN SAID CAVITY ABOUT AND SPACED FROM SAID CENTRAL BOSS, SAID MEANS INCLUDING A WASHER OF FLEXIBLE, INSULATING MATERIAL INTERPOSED BETWEEN SAID POT CORE AND SAID WINDING, AT EACH END OF SAID WINDING, SAID WASHERS HAVING SERRATIONS ABOUT THE INNER AND OUTER DIAMETERS THEREOF, ALL OF SAID INNER SERRATIONS AND MOST OF SAID OUTER SERRATIONS BEING BENT AND DISPOSED BETWEEN SAID WALLS AND SAID WINDING.
 2. AN ADJUSTABLE INDUCTOR, ACCORDING TO CLAIM 1, WHEREIN: SAID LEAD-OUT WIRES EXTEND RADIALLY AND ARE DISPOSED WITHIN THE SERRATIONS OF SAID OUTER DIAMETER. 